#include <iostream>
#include <cstring>
#include <algorithm>

using namespace std;

int main()
{
    int T;
    cin >> T;
    while (T -- )
    {
        int n;
        string s;
        cin >> n >> s;
        sort(s.begin(), s.end());
        cout << s << endl;
    }
    return 0;
}